investigate 'needscomma' in json printer

[job]

from notes from @pschoenm:

fixed issue when running bgpq3_print_json_prefixlist multiple times, creates a comma at the beginning of json. the variable needscomma should really be a pointer that is passed to the functions during printing. for now hacked it to initialize the variable at the start of a print that uses it.

[job]

possible patch

diff --git a/bgpq3_printer.c b/bgpq3_printer.c
index 2842b06..64f1844 100644
--- a/bgpq3_printer.c
+++ b/bgpq3_printer.c
@@ -701,6 +701,8 @@ int
 bgpq3_print_json_aspath(FILE* f, struct bgpq_expander* b)
 {
 	int nc=0, i, j, k;
+
+	needscomma = 0;
 	fprintf(f,"{\"%s\": [", b->name?b->name:"NN");

 	for(k=0;k<65536;k++) {
@@ -1231,6 +1233,7 @@ bgpq3_print_cisco_prefixlist(FILE* f, struct bgpq_expander* b)
 int
 bgpq3_print_ciscoxr_prefixlist(FILE* f, struct bgpq_expander* b)
 {
+	needscomma = 0;
 	bname=b->name ? b->name : "NN";
 	fprintf(f,"no prefix-set %s\nprefix-set %s\n", bname, bname);
 	sx_radix_tree_foreach(b->tree,bgpq3_print_cprefixxr,f);
@@ -1241,6 +1244,7 @@ bgpq3_print_ciscoxr_prefixlist(FILE* f, struct bgpq_expander* b)
 int
 bgpq3_print_json_prefixlist(FILE* f, struct bgpq_expander* b)
 {
+	needscomma = 0;
 	fprintf(f,"{ \"%s\": [",
 		b->name?b->name:"NN");
 	sx_radix_tree_foreach(b->tree,bgpq3_print_json_prefix,f);
@@ -1251,6 +1255,7 @@ bgpq3_print_json_prefixlist(FILE* f, struct bgpq_expander* b)
 int
 bgpq3_print_bird_prefixlist(FILE* f, struct bgpq_expander* b)
 {
+	needscomma = 0;
 	if (!sx_radix_tree_empty(b->tree)) {
 		fprintf(f,"%s = [",
 			b->name?b->name:"NN");